Sand production is a major problem in the oil and gas industry. Loss of production, sand disposal issues, the need for routine cleanouts, damage to well jewelry, and stuck well accessories are the most common reasons for setbacks caused by sand production. The sand control methods yield the most desirable results when are implemented early in the life of a well before sand production becomes a problem because of the onset of water production or before formation damage occurs as a result of formation disturbances or subsidence. For the wells that start sand production at a later stage, workover with conventional gravel packing is one way to alleviate the problem, but such a costly undertaking is not always economically justifiable.
The candidate field is located at offshore Terengganu in Malaysia and has been in production since 1982. The reservoir consists of several layers, including the unconsolidated (J-sand) layer. Well A, for which the initial producing intervals were isolated, was recompleted in the J-sand layer by March 2005 and started producing 250 BOPD. Unfortunately, the well could only produce for 3 months before it was shut-in due to severe sand production. The well had been shut in for 4 years and even after a series of coiled tubing operations to perform sand cleanout, it was not possible to flow the well for a single day.
Because of the marginal reserves available and the high cost of mobilizing a workover rig to perform a conventional gravelpack completion, the operator chose to recomplete the well using a rigless technique that allowed the gravel pack to be placed through the existing completion tubing.
To ensure the best possible perforation packing efficiency and annulus pack quality, the "vent screen and isolation packer" through-tubing gravel pack (TTGP) technique was used. After the TTGP operation, production stabilized at about 180 BOPD. This method can be considered for the wells that are shut-in because of severe sand production and the wells that are producing at restricted production rates due to sanding problems.
Similar to most of the early fields developed in the Malay basin, all the wells in the candidate field were completed without any sand control measures. Sand production was not expected under the normal drawdown planned. Nonetheless, as the field has aged and with a higher drawdown profile, sand production has significantly increased. Examination of the drawdown profile of the current unconsolidated (J-sand) layer in connection with the reservoir rock properties was conducted to obtain a better understanding of the reservoir. The compressional travel time of the J-sand, based on the available sonic log data, was at 110 µsec/ft, clearly in the critical region for sanding to occur. In addition, based on the simulated drawdown profile, the critical drawdown pressure for the J-sand layer was 150 psi. With the current flowing profile and reservoir pressure depletion, the simulated drawdown was already beyond the 520-psi limit and this led to the likelihood of the wellbore sand matrix to fail.
With only 3 months of production, the potential of the J-sand layer in well A (Figure 1) was far from abandonment. The reserve assessment still found the well's production to be economical, even though, the volume was marginal. As a result, several rigless remedial sand control methods for mature fields were considered. The following discussion presents an overview of the various techniques that are currently being used within the industry, which were accounted for well A.